Betaines of the formula: ##STR2## wherein R.sub.1 is a long chain alkyl group, R.sub.2 is a short chain alkylene group, and n is an integer from 1 to 3 are known, and they are known to be useful in shampoo compositions. These specific betaine compounds and their preparation are discussed in U.S. Pat. Nos. 2,866,423 and 3,225,074 and in West German Pat. No. 1,062,392; and the latter also discloses the use of such compounds in shampoo and bubble bath preparations. Related compounds are also disclosed in U.S. Pat. No. 2,777,872 and in U.S. Pat. No. 2,961,451.
The betaine compounds are disclosed as prepared by the reaction of an amidotertiary amine of the formula: ##STR3## wherein R.sub.1 and R.sub.2 have the meanings stated above with an alkali metal salt of a short chain chloroalkanoic acid, such as chloroacetic acid, in an aqueous medium, or in a medium which includes water and an organic solvent.
An alkali metal chloride, such as sodium chloride, is produced as a co-product in the process, and this co-product is difficult or expensive to remove from substantially aqueous reaction media.
Other betaine surfactants are made in a similar manner by the substitution of other tertiary amines having at least one long chain aliphatic radical attached directly to the amino nitrogen atom for the amidotertiary amine of the above formula.
The betaine products have desirable foaming and cleansing properties, and are generally regarded as being mild in their action. They, however, result in compositions that are inherently moderately irritating to the eyes when used at concentrations normally considered effective in enhancing foaming and conditioning properties of commercial shampoo.